Brake pedal to the floor.

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hawaii_620
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Joined: Mon Jul 05, 2010 4:52 am
Car: 75 Datsun 620

Brake pedal to the floor.

Postby hawaii_620 » Mon Jul 05, 2010 5:31 am

I posted this as a reply to the "Disc Brake Conversion" thread, but thought it ought to have it's own thread. Please read below:

I've done the same conversion with the brackets bought on ebay. Everything fit fine. But now I'm having a problem with my brake pedal sinking all the way to the bottom of the floor if the booster lines are hooked up.

Here is what I did so far:
I changed out the master cylinder to a new 280zx, new brake booster and rebuilt back drum setup completely. I've bleed the master on a bench (I think I did it correctly, don't know if I pushed the rod in far enough), but did the "two tubes back in the reservoir, till no bubbles" thing. Bleed the brake system with a friend, two man system, on all the brake lines with no bubbles. Pedal doesn't get firm till about almost half way down with the truck off (no booster assist), with the truck running, the pedal sinks to the floor. It does grab the brakes when at the bottom but not convincingly.

I don't know what else to do. Any tips on what to double/triple check again would be much appreciated as this has got me stumped.

I was reading on other forums that there are two different types of Master Cylinders, one that is made for a brake booster and one that is non-booster? Is this correct and could this be the problem?


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Rev_D21
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Re: Brake pedal to the floor.

Postby Rev_D21 » Wed Jul 07, 2010 5:19 pm

Calipers on the correct sides with the bleeders pointing upwards?

hawaii_620
Posts: 17
Joined: Mon Jul 05, 2010 4:52 am
Car: 75 Datsun 620

Re: Brake pedal to the floor.

Postby hawaii_620 » Wed Jul 07, 2010 7:13 pm

Yes, they are on the correct side.

My newest theory is that the push rod from the brake booster isn't long enough to make good travel in the 280zx master cylinder. Does anyone know if the push rod in the brake booster for the 620 is adjustable? I don't want to start spinning or twisting something that isn't meant to be.

dfresh777
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Location: Portland, OR
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Re: Brake pedal to the floor.

Postby dfresh777 » Thu Jul 15, 2010 8:36 pm

I believe it is, but i will check it out

hawaii_620
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Joined: Mon Jul 05, 2010 4:52 am
Car: 75 Datsun 620

Re: Brake pedal to the floor.

Postby hawaii_620 » Fri Jul 16, 2010 1:58 am

If you could find out about the booster push rod being adjustable that would be great! Someone told me to try and bleed the front with the calipers removed. So that the piston could fully be pushed out i guess, to get possibly any air trapped inside out. What do you guys think of that? Should I try that?

dfresh777
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Car: Datsun 620 Pickup
Location: Portland, OR
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Re: Brake pedal to the floor.

Postby dfresh777 » Fri Jul 16, 2010 5:37 pm

The rod into the break booster is adjustable, i suggest leaving your pads and everything together and have someone pump the break and hold it and see if you get an air bubbles when you release the bleeder. i suggest using clear hose so you can see the fluid go into a plastic bottle or something.

hawaii_620
Posts: 17
Joined: Mon Jul 05, 2010 4:52 am
Car: 75 Datsun 620

Re: Brake pedal to the floor.

Postby hawaii_620 » Sat Jul 17, 2010 3:00 am

Hey dfresh777, thanks for the info on the push rod, I'm going to fuss with it this weekend. :dblthumb:

I lived in Portland for a little while, up on 22nd and Johnston. Portland was and will always be my favorite city to live in. Love the Streetcar and MaxRail!

hawaii_620
Posts: 17
Joined: Mon Jul 05, 2010 4:52 am
Car: 75 Datsun 620

Re: Brake pedal to the floor.

Postby hawaii_620 » Fri Jul 23, 2010 2:24 pm

Adjusted the push rod. It wasn't very hard to adjust either. I just loosened the master, gently pulled it to the side, removed the spacer and then removed the push rod. And with a gentle tug, removed the rod. I think that was the problem. It was too short and had a lot of "free" space to travel before pushing the plunger in the master cylinder. I haven't given it a road test yet, but my brake pedal already feels 100% better. I'll take it for a spin this weekend and give the follow up on.


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